The present invention relates to an arrangement for the stepwise feed of band material with two oppositely driven feed rollers, whereby a first feed roller is locally fixedly supported and a second feed roller is adapted to be moved alternately toward the other feed roller, respectively, away from the latter into a return position by means of a lifting device at the instant of the reversal of the direction of rotation, whereby the second feed roller is rotatably supported in a rocker, at one end of which engages a guide element of the lifting device and at whose other end which is located opposite with respect to the axis of the second feed roller, a spring force storage device engages in the direction of the pressure of the second feed roller at the first feed roller.
Arrangements of this type operate at the rhythm, for example, of a press and serve to feed band material to the tool in the press. It is necessary in connection therewith to discontinuously feed the band material in identical band lengths. It is further necessary depending on the type of the work tool, for example, with the use of multiple press tools, to operate in the lower dead-center position of the press ram with an intermediate clearing of the feed rollers and of the pressure device. Therebeyond, the feed arrangement is to be operated with band materials of different thicknesses.
A feed arrangement without free-wheeling devices and brakes for the feed rollers to be used, is described in the DE-PS 22 41 686 in which the band material is held fast during the feed pauses and is released during the feed phases. The arrangement thereby provides two mutually oppositely driven feed rollers, of which a first feed roller is locally fixedly supported and a second feed roller is movable in each case at the instant of the reversal of the direction of rotation toward the other feed roller, respectively, away from this feed roller into a return position by means of a lifting device. The second feed roller is thereby rotatably supported on a rocker. The lifting device engages at one end of the rocker by way of a guide element while a compression spring engages at the other end thereof which is effective in the direction of action of the contact pressure of the second feed roller at the first feed roller. A guide member locally fixedly supported is connected with the rocker between the second feed roller and the point of engagement of the compression spring. A pressure device is taken along together with the guide member which is guided against a locally fixed counter device in the return position of the second feed roller for purposes of holding fast the band material. The guide element is placed by way of a cam follower against a control cam which is rotated directly by the main drive. The rotary movement of the feed rollers is oscillating to and from by way of a connecting rod drive variable as regards the amplitude of the rotary movement. The rocker is supported on both ends by springs. The springs bring about a pivoting of the rocker into the return position with a corresponding cam follower position whereby the second feed roller is lifted off from the band material whereas the pressure device is guided against an abutment under interposition of the band material. During the further pivoting of the rocker, the latter can selectively run up against a pivot point whereby the pressure device can be lifted off at the same time for purposes of an intermediate lifting or clearing. By changing the pivotal connection of the guide element, the feed arrangement can be used for different band material thicknesses. The spring for returning the cam follower along the cam operates during the start of the intermediate clearing mechanism against the abutment spring for the second feed roller whereas both springs engage together at the rocker in one direction of action until the rocker runs up on the pivot point. Differently thick band materials require a manual readjustment of the feed arrangement and they produce thereby different spring forces. A thicker band material increases the pressure or abutment force of the second feed roller whereas the force of the spring acting opposite this spring is reduced in the point of pivotal connection of the guide element.
In contradistinction thereto, it is the object of the present invention to positively guide the movements of the rocker into the forward and return positions.
The underlying problems are solved according to the present invention in that a guide member engages at the rocker between the second feed roller and the point of engagement of the guide element which is locally fixedly and rotatably supported with its other end at approximately the height of the center of the second feed roller, in that a pressure device is connected with the guide member which in the return position of the second feed roller is pressed against a locally fixed counter device under interposition of the band material for holding fixed the band material during the return movement of the first feed roller, and in that a connecting rod engages at the guide element spaced with respect to the point of engagement thereof at the rocker, which is to be driven essentially parallel to the rocker and extending in the direction thereof in a locally fixed bearing support by way of an eccentric.
It is thereby of particular advantage that the feed rollers open and close during standstill of the band material and that with a change of the thickness of the band material and consequently with a required matching of the lifting device, the operating conditions of the lifting device constructed in the manner of a four joint system, do not change. The band feed arrangement is independent of band thickness. The abutment and lifting movements of the second feed roller and of the pressure device at, respectively, away from the band material and the abutment of the guide element at a locally fixed stop takes place by the movement of a single adjusting device.